A car laden with explosives detonated outside the United Nations’ main office in Nigeria’s capital Friday, blowing part of the concrete structure into shards and killing an undetermined number of people.

Witnesses told The Associated Press that a sedan broke through the exit at the U.N. compound, ramming through two separate gates as guards tried to stop the vehicle. The suicide bomber inside drove the car just up to the main reception of the building before detonating, inflicting the most damage possible, witnesses said.

“I saw scattered bodies,” said Michael Ofilaje, a UNICEF worker at the building. “Many people are dead.”

He said it felt like “the blast came from the basement and shook the building.”

The building houses about 400 employees of the U.N. in Nigeria, including the majority of its offices. A local U.N. spokesman declined to comment, but a local hospital administrator told the AP it had treated as many as 40 victims so far, with more people coming in.

Alessandra Vellucci, a spokeswoman for the U.N. office in Geneva, confirmed that the global body’s offices in Abuja had been bombed.

She told the AP that there was no word yet on casualties.

U.N. deputy spokesman Farhan Haq in New York said, “There are some indications of fatalities, but we are trying to get confirmation.”

The building, located in the same neighborhood as the U.S. embassy and other diplomatic posts in Abuja, had a huge hole punched in it. Workers brought three large cranes to the building by midday Friday, trying to pull away the concrete and rubble to try and find survivors. Others at the site stood around, stunned, as medical workers began carrying out what appeared to be the dead.

“This is getting out of hand,” said a U.N. staffer who identified himself as Bodunrin. “If they can get into the U.N. House, they can reach anywhere.”